Gallium nitride-based III-V nitride, which is attracting attention as an excellent blue light emitting element, is put into practical use in light emitting diode field, and expected also as a light pick-up blue-violet semiconductor laser element. In a process for growing a gallium nitride single crystal by Na flux method, a mixed gas of nitrogen and ammonia is used with an atmospheric pressure of 10 to 100 atoms, for example, in Japanese Patent Publication No. 2002-293696A. In Japanese Patent Publication No. 2003-292400A, also, the atmospheric pressure during the growth is 100 atm or less, with 2, 3, and 5 MPa (about 20 atm, 30 atm and 50 atm) being used in the working examples thereof.
On the other hand, the applicant disclosed a method for efficiently growing a gallium nitride single crystal under a specific condition by use of a hot isostatic pressing (HIP) apparatus in Japanese Patent Application No. 2004-103093 (WO 2005/095682 A1).
It is described in “Growth of Large/Low-Dislocation GaN Single Crystal by LPE Growth” by Kawamura et al. in “Journal of Japanese Association for Crystal Growth” Vol. 32, No. 1, 2005 that when a GaN single crystal is grown by Na flux method, the GaN single crystal is susceptible to blackening due to existence of nitrogen defects.
It is also described in Japanese Patent Publication No. 2005-132663A that in growth of a nitride single crystal in a flux containing lithium, a reaction vessel which contacts with the flux is formed of metallic tantalum to thereby prevent breakage of the reaction vessel.